Continuous positive airway pressure device

ABSTRACT

A continuous positive pressure device which includes an air reservoir connected to a delivery device (e.g. mask or mouthpiece) by an air supply hose; the reservoir includes a rigid protective housing and a plate which applies uniform pressure on the reservoir irrespective of its degree of inflation; the plate is connected to the housing by a non distorting and expandable frame which can expand or contract to permit movement of the plate only in a single plane, as the reservoir inflates or deflates.

TECHNICAL FIELD

[0001] The present invention relates to a continuous positive airwaypressure (CPAP) device, i.e. a device for supplying air or (moreusually) an air/oxygen mixture at a positive (i.e. above atmospheric)pressure, to a patient, and to an air reservoir apparatus for such adevice. A CPAP machine may assist the lung function of a sick or injuredpatient by supplying air, generally oxygen enriched, at anabove-atmospheric pressure, and/or may actively assist carbon dioxideremoval from the lungs by using two levels of positive pressure. In thelatter mode, the device functions as a ventilator and is capable ofproviding up to 100% of a patient's minute ventilation.

BACKGROUND ART

[0002] A number of continuous positive airway pressure devices arealready known. Devices of this type currently being used in hospitals infirst world countries generally require the supply of oxygen at highflow rates; since most modem hospitals have oxygen on tap and oxygen isavailable cheaply, a relatively wasteful use of oxygen is acceptable.However, in less developed countries or in out-of-hospital situations,(e.g. in ambulances, on battlefields, in emergency treatment stations)oxygen is available only in cylinders and a high rate of use of oxygenis unacceptable:—the cylinders simply are emptied too quickly.

[0003] It is therefore an object of the present invention to provide acontinuous positive airway pressure device capable of operating at lowflow rates of oxygen, whilst nevertheless reliably supplying therequired air/oxygen mix to a patient.

[0004] In order to reduce the rate of the use of oxygen, it is necessaryto use a reservoir built into the device. This is because the peak gasflow requirements of patient in acute respiratory distress can beanything from 60-120 litres per minute but practical engineeringconsiderations mean that the gas flow rate through a portable continuouspositive airway pressure device should be kept below 30 litres perminute. To make up the difference between gas demand and gas supply,portable devices must employ a storage system to store the gas while thepatient is in between breaths or is breathing out. Any such storagesystem must be capable of a substantially constant pressure response,i.e. the pressure of the gas supply to the patient must not varysubstantially whether the reservoir is full, part full or nearly empty.

[0005] A number of existing devices use a balloon reservoir made ofelastic material or a reservoir shaped like an old-fashioned fire sidebellows. Both of these designs have the drawback that the pressure ofthe gas supply to the patient varies considerably depending upon whetherthe balloon/bellows is nearly full, partly full or nearly empty. Toovercome this drawback, a very much larger reservoir has to be used thanis optimal for a portable device.

[0006] Some designs have been proposed to overcome this problem byproviding a constant pressure response reservoir; see for example GermanPatent No.s DE 3712389 and EP 0744184.

[0007] German patent No DE 371-2389 discloses a reservoir of flexiblematerial the upper surface of which is weighted either by a weight or bya weighted lever. However, the reservoir does not incorporate any typeof stabilizing device to ensure that, as the bellows is compressed andexpanded, the weighting on the reservoir is kept even.

[0008] EP 0744184 discloses a reservoir at least partly of elasticmaterial, preformed so that the reservoir itself supplies compression toits contents. Since the pressure applied by a reservoir of this designwould fluctuate markedly depending upon the volume of gas contained inthe reservoir (i.e. according to the degree of expansion of thereservoir) a reservoir of this design could not provide a gas at auniform or substantially uniform pressure.

[0009] A further drawback to both of the above described designs is thatthey relate to relatively large and complex devices which would beunsuitable for use outside a hospital environment.

[0010] Russian patent 459243 and German patent DE 410-7666 both disclosea reservoir in the form of simple bellows which is weighted by an uppermoving plate. The moving plate can slide towards or away from abaseplate along fixed vertical guides. The guides are rigid and extendthe full height of the expanded reservoir, resulting in a bulkyapparatus which cannot be regarded as portable except in a hospitalenvironment.

[0011] Indeed, a marked drawback of all known designs is the bulk of theequipment. Some of the devices, of course, are not designed to beportable at all, but even those devices which technically are portableare relatively large, fragile and easily damaged. A device which isclassed as “portable” for a hospital environment may nevertheless becompletely unsuited to being thrown into the back of a truck or into anaircraft, and may be too bulky to be stored conveniently for emergencyuse.

DISCLOSURE OF INVENTION

[0012] It is therefore a further object of the present invention toprovide an air reservoir apparatus which can be incorporated into acontinuous positive airway pressure device which can be stowed into arelatively small space and which is robust and easily portable when notin use.

[0013] The present invention provides an air reservoir apparatus for acontinuous positive airway pressure device, the air reservoir apparatuscomprising: a rigid housing protecting an air reservoir; a platearranged to apply a uniform pressure on the air reservoir, irrespectiveof the degree of inflation of the air reservoir, said plate beingconnected to the housing by a substantially non-distortable expandableframe, which can expand or contract to permit movement of the plate onlyin a single plane, as the air reservoir respectively inflates ordeflates.

[0014] As used here in, the term “air” includes air, oxygen, air/oxygenmixtures and mixtures of air and/or oxygen with other gases and withtherapeutic drugs or gene therapy or other preparations.

[0015] Preferably, the plate is formed as one side of the housing, sothat when the air reservoir is deflated, the plate can be secured to thehousing to completely enclose the air reservoir. The plate may be asolid sheet of material or, if it is not necessary for the plate to bedust proof, may be formed from a rigid mesh or other openwork material.

[0016] Preferably also, the air reservoir is made of a flexiblenon-elastic material.

[0017] The present invention further provides a CPAP deviceincorporating the above-described air reservoir apparatus connected byan air supply hose to a delivery device.

[0018] Gas supply to the device of the present invention can bedelivered by any suitable gas delivery system, which includes, but isnot limited to:—compressed air and/or oxygen from a piped system or froma cylinder; fan forced air and/or oxygen, supplied by any of a range ofknown equipment; compressed air/oxygen from a portable reservoir. Itshould be noted that a portable reservoir can be devised from any largecapacity inflatable object, even one which is hand pumped e.g. aninflatable mattress.

[0019] The device may be used with standard bore hose (internal diameterapproximately 22 mm). However, it is preferred to use the device of thepresent invention with a wide bore hose (i.e. a hose of diameter between30-55 mm internal diameter), since the combination of the device andwide bore hose provides apparatus in which the imposed work of breathingon a patient is independent of the fresh gas flow rate.

[0020] A further aspect of the present invention is that the abovedescribed device, used in combination with wide bore hose, may be usedto deliver drug therapy and gene therapy, and hyperbaric treatments, andto provide portable CPAP to treat altitude sickness and acute pulmonaryoedema (e.g. heart failure and lung injury).

[0021] The device also is useful in intra-/post-operative applicationswhere the patient has an increased oxygen requirement, (typically due tosmall areas of lung collapse). Further, the device is useful in thetreatment of all cases of chronic airflow limitation or chronic airwaysdisease (e.g. asthma).

[0022] For emergency/battlefield use, the device may be fitted withchemical absorbent or bacterial/viral/other biologically active particlefilters, to protect the patient from toxic gases and/or biologicalweapons.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] By way of example only, a preferred embodiment of the presentinvention is described in detail with reference to the accompanyingdrawings, in which:—

[0024]FIG. 1 is a diagrammatic plan view of the device of the presentinvention set up for use;

[0025]FIG. 2 is a plan view of part of the device of FIG. 1 on anenlarged scale;

[0026]FIG. 3 is an isometric view of the support framing of the deviceof FIG. 2, on an enlarged scale;

[0027]FIGS. 4 and 5 are sectional side views through the device of FIG.2, showing the device in use;

[0028]FIGS. 6 and 7 are diagrammatic side and plan views respectively ofa preferred weighting device;

[0029]FIG. 8 is an exploded side view of a mounting clip;

[0030]FIG. 9 is a front view of the clip of FIG. 8;

[0031]FIGS. 10 and 11 are sectional side views through a device similarto that of FIG. 2, but with a different type of support framing; and

[0032]FIG. 12 is a diagrammatic sectional side view of a modified formof the device of the present invention.

BEST MODES OF CARRYING OUT THE INVENTION

[0033] Referring to FIG. 1 of the drawings, a device 2 in accordancewith the present invention comprises an air reservoir apparatus 3 (shownin outline only), which in use is connected by an air supply hose 4 to adelivery device in the form of a facemask 5. The facemask 5 may be ofany suitable known type and does not form part of the present invention.

[0034] Different delivery devices may be used, depending upon thecircumstances. For example the delivery device may be a nasal mask or amouthpiece (optionally in combination with a nasal clip) or even anendotracheal or tracheotomy tube.

[0035] The air reservoir apparatus 3 is shown in greater detail in FIGS.2-5. The apparatus 3 comprises a housing 6 which contains a supportframing 7 surrounding an air reservoir 8. The housing 6 is in the formof a shallow rectangular case with parallel, opposed flat sides 9,10.The side 10 is formed separately from the rest of the housing, and issecured to the housing only by the support framing 7 and by four catches11 located at the corners of the housing (FIG. 2 only).

[0036] In use, the housing 6 lies flat on side 9 and the catches 11 arereleased so that the side 10 can move towards and away from the side 9as indicated by arrows A and B in FIGS. 4 and 5. The housing 6 may bemade of any tough, impact resistant, lightweight material; preferably,the sides 9,10 are made of a transparent material.

[0037] The side 10 is weighted or fitted with removable weights, up to atotal weight of about 4 kg. The weighting may be achieved in anyconvenient manner:—for example, the side 10 could be made of a heavymaterial and/or could be fitted with weighted strips (not shown) alongits edges and/or could be provided with pockets on its upper or lowersurfaces into which weights could be inserted. Preferably, the weightingsystem illustrated in FIGS. 6 and 7 is used, as hereinafter described.However, it is preferable (but not essential) that the side 10 isweighted evenly.

[0038] An access port 12 is formed in one of the sides 9,10, to allowaccess into the interior of the housing 6. The port 12 may be formed ineither of the sides 9,10; in the embodiment illustrated, the port 12 isformed in side 10. The port 12 consists of a circular frame 13 which isrigidly secured around the edge of aperture formed in side 10, and aplate 14 which is externally screw threaded to engage a correspondingscrew thread formed on the inner surface of the frame 13. When the plate14 is screwed in place, the port 12 is substantially dust proof.

[0039] The support framing 7 connects the movable side 10 to the fixedside 9 in such a way that the movable side 10 can move only in a singleplane and at all times during its movement towards or away from the side9 remains parallel to the side 9. Thus, the support framing 7 mustprovide a rigid and non-distorting hinge which supports the movable side10 evenly.

[0040] As shown in FIG. 3, the support framing 7 comprises a firstrectangular frame made from two pairs of parallel opposed rods 66,67secured between corner blocks 68, and a second rectangular frame madefrom two pairs of parallel opposed rods 69,70 secured between cornerblocks 71. The first and second frames are spaced apart in a directionperpendicular to the planes of the rectangles, and interconnected byeight pairs of hinge arms 72,73, as hereinafter described.

[0041] In the rectangular frames, each of the corner blocks 68,71comprises a cuboid block with a ball bearing (not visible) set into eachof two adjacent sides 68 a, 68 b, 71 a, 71 b. The rods, 66,67 of thefirst frame and the rods 69,70 of the second frame are mounted in thebearings of the corresponding blocks.

[0042] The support framing 7 shown in FIG. 3 is mounted between theparallel opposed sides 9,10 of the air reservoir apparatus housing (seeFIGS. 4 and 5) with the side 10 rigidly secured to the upper surface 68c of each of the blocks 68, and the side 9 rigidly secured to the lowersurface 71 c of each of the blocks 71.

[0043] Each pair of hinge arms 72,73 consists of a flat plate which ispivotally mounted on the corresponding rod at one end, and pivoted tothe other hinge arm at the other end. Each pair of hinge arms 72,73 ismounted between the first and second frames adjacent the blocks 68,71.Each pair of arms is formed with a stop (not shown) to prevent the hingefrom over extending i.e. moving to, or close to, a position in which thetwo plates of the hinge lie in the same vertical line, since this wouldjam the hinge and prevent it from collapsing.

[0044] In use, the support framing 65 provides a rigid andnon-distorting hinge which connects the movable side 10 to the fixedside 9 in such a way that the movable side 10 can move only in a singleplane and at all times during its movement towards or away from the side9 remains parallel to the side 9. The pairs of hinge arms 72,73 maintainthe first frame in a plane parallel to that of the second frame at alltimes during movement, and the arrangement of two pairs of hinge armsbetween each opposed pair of rods in the first and second framesprevents any swaying or distortion of one frame relative to the other.

[0045] The configuration and arrangement of the frame 7 described abovewill expand and contract easily, with minimal friction. Further, becausethe frame 7 is braced at each corner by the blocks 68, 71, the framewill not distort or wobble even when fully extended as shown in FIG. 5.This stability is very important, because in use the side 10 appliespressure to the air reservoir 8, as hereinafter described, and if theframe 7 distorts or sways to one side or the other, the pressure appliedto the reservoir 8 will be uneven. It is important that the frame 7maintains this stability even when subject to external forces, e.g. whenthe device is being used in a moving vehicle.

[0046] The frame 7 could have a different shape in plan (e.g. triangularor hexagonal) and/or a different cross sectional shape, but it isimportant that, whatever the shape of the frame, it remains stable andundistorted in all positions.

[0047] The air reservoir 8 is a bag made of a flexible butnon-extensible sheet material such as Mylar; preferably the material istransparent. The air reservoir 8 is formed with a series of concertinapleats around its edge, so that the collapsed reservoir lies flat, butthe expanded reservoir retains its shape. Each of the inner folds 8 a ofthe reservoir is reinforced by the stiffening rib (shown in FIG. 5 only)which extends around the outside of each inner fold, to ensure that thereservoir keeps its shape even when expanded.

[0048] It would be possible to build stiffening ribs or other internalsupport into the air reservoir itself, rather than using separateexternal ribs.

[0049] Instead of, or in addition to, the stiffening ribs, the airreservoir 8 may be held in shape by internal reinforcing webs made ofthe same material as the reservoir. These webs may be arranged as spacedparallel sheets extending across the width of the reservoir, which aretensioned as the reservoir expands, and so hold it in shape.

[0050] By using a non-extensible material to form the reservoir andusing a vertically ascending to weight virtually no energy is lost asheat to the reservoir bag. This contrasts with current devices that userubber materials and/or sprung bellows systems. This therefore minimizesany additional work of breathing imposed by this invention.

[0051] The air reservoir 8 has a tubular inlet 22 formed integrally withthe bag at the lower surface of one end of the bag. The inlet 22 maysimply be push fated onto a connector tube 23 which is fitted through anaperture 24 in the housing 6. Preferably, however, the inlet 22 ismounted using a mounting clip as shown in FIGS. 8 and 9.

[0052]FIGS. 8 and 9 show views of the inlet 22 of the air reservoir 8,with the housing cutaway for clarity. As described above, the inlet 22is a short tube secured to, or formed integrally with, the air reservoir8. The inlet 22 is formed with a rim 90 around its outer edge (FIG. 8only); this rim 90 is pushed fitted into a U-shaped channel 91 formed inone portion of a mounting clip 92.

[0053] The mounting dip 92 is also U-shaped in side view:—one arm of theU provides the channel 91, and the other consists of an outwardly convexplate 93 formed with a centre hole 94 of the same diameter as the inlet22, for access to the inlet 22 by the connector tube 23.

[0054] The mounting clip 92 is pivotally mounted in the housing on apivot (not shown) at the base of the U, such that the clip 92 can pivotbetween the position of FIG. 8 and a position at 90° to FIG. 8 position.In the position of FIG. 8, the inlet 22 is accessible and can beconnected to the connector tube 23. In the position of FIG. 9, the inlettube is folded flat onto the side 9, with the plane of the inlet 22 andthe channel 91 parallel to the plane of the side 9. In this position,the plate 93 dips over the adjacent edge of the side 10 of the housing,to hold the housing closed.

[0055] The advantage of the mounting clip 92 is that it reduces thethickness of the housing 6 in the closed position:—the diameter of theinlet 22 cannot be reduced, because this would restrict the flow of gasout of the air reservoir 8. Thus, the housing 6 in the closed positionmust accommodate the diameter of the inlet 22, resulting in a relativelybulky housing unless the inlet 22 can be turned through 90 degrees byusing the clip of the present invention.

[0056] The inlet 25 from the oxygen/air supply is formed in theconnector tube 23 adjacent the housing 6. The other end of the hose 4 isa push fit on the inlet 26 of the mask 5. The hose 4 is a tough, verylight, flexible wire reinforced wide bore hose, preferably made oftransparent material; typically, the tube would have a diameter of theorder of 41 mm. The wire reinforcing prevents kinking of the hose andallows the hose to be compressed along its length, for compact storage.The use of a wide bore hose is important because this minimizes thepressure drop that occurs with transient high flows during inspirationobviating the need for high fresh gas flows. Hose typically used inpresent continuous positive airway pressure devices has an internaldiameter of 22 mm; thus, comparatively speaking, the wide bore hose usedin this invention gives only about {fraction (1/16)} of the pressuredrop in conventional breathing hoses. As a result the additional work ofbreathing imposed by the breathing circuit is minimized.

[0057] The use of wide bore hose has the further advantage that thedevice also can be used to deliver to the patient's lungs any agentwhich can be delivered using metered dose inhaler technology. The agentis delivered through a port 27 in the hose 4. This technique is notlimited to agents related directly to the lungs:—providing the productis one which can be absorbed by the lungs, other parts of the body canbe treated via systemic absorption.

[0058] Agents which can be administered through metered dose inhalationinclude (but are not limited to) drugs such as bronchodilators, genetherapy agents, and appropriately packaged proteins, peptides andmacromolecules.

[0059] Metered dose inhaler agents cannot be effectively administeredthrough continuous positive airway pressure devices which operate athigh fresh gas flow rates because too high a proportion of the agent isswept straight through the device entrained in the gas, and is notpassed through to the patient. With this invention the fresh gas flowrates may be as low as the patient's minute ventilation which is about 5to 10 litres per minute.

[0060] Rather than simply weighting the side 10 of the device by makingit of a heavy material, or fitting it with weighted ships or similardevices, preferably the weighting device shown in FIGS. 6 and 7 is used.

[0061] As shown in FIGS. 6 and 7, the side 10 has a springloaded drum 80mounted in the centre thereof. The drum 80 can be rotated in a clockwisedirection to reduce tension and in a is counter clockwise direction toincrease tension; preferably, the upper surface of the drum is marked asa dial (not shown) so that a user can select the tension settingrequired.

[0062] A first cable 81 is anchored at one end to a point 82 on thelower side 9 of the housing, led around a pulley 83 secured to theunderside of the side 10, and secured to one side of the circumferenceof the drum 80. A second cable 81 a is anchored at one end to a point 85on the lower side 9 of the housing, led around a second pulley 84secured to the underside of the side 10 on the opposite side of the drum80 to the pulley 83, and secured to the opposite side of thecircumference of the drum 80. The anchorage points 82,85 are locatedvertically below the pulleys 83,84.

[0063] The cables 81,81 a, are made of a tough but non-elastic substancewith a high resistance to abrasion (e.g. Kevlar).

[0064] The spring loading on the drum 80 tensions the cables 81,81 a;the spring loading is adjusted by rotating the drum 80 as describedabove. When the air reservoir 8 (not shown) is inflated to move the side10 away from the side 9, supported by the support framing 7 (showndiagrammatically only), the cables 81,81 a rotate the drum 80 againstthe force of the spring loading. Thus, the force of the spring loadingpulling against the cables 81,81 a pulls the side 10 towards the side 9,acting as an equivalent to weighting the side 10.

[0065] The above described device is used as follows:—the housing 6 issupported on its side 9, and the catches 11 are released so that theside 10 is free to move away from the side 9. The weighting on the side10 (e.g. the loading imposed by the springloaded drum 80) is adjusted inaccordance with the level of continuous positive airway pressurerequired. A higher pressure requires extra weighting. A supply of oxygen(typically from a cylinder 30 at a pressure of 150 atmospheres regulateddown to 4 atmospheres at the cylinder outlet) is connected to a Venturi31 and to a humidifier 32 and then to the inlet 25. The oxygen/air mixadmitted through the inlet 25 fills the hose 4 and inflates the airreservoir 8, pushing the side 10 away from side 9, in the direction ofArrow B (FIGS. 4 and 5). The pressure in the reservoir and hose dependsupon the back pressure in the system, which is governed by theresistance of the exhaust valve 33. Typically the air pressure in thereservoir is of the order of 5 to 30 cm of water. To avoid overpressuring the system, and causing patient injury, a pressure reliefvalve 34 is fitted in the hose 4.

[0066] The Venturi 31 extrains room air which mixes with the oxygen fromthe cylinder 30. The mixture may vary between 30% oxygen and 100% oxygendepending upon the patient's condition. Preferably, the Venturi outflowis through a threshold resistor valve set at a level above the CPAPlevel. The Venturi 31 may be replaced by any of a range of air/oxygenblending devices. However, these blenders require an additional highpressure medical-grade air supply.

[0067] The use of a humidifier 32 is optional. However, if a humidifier32 is used, it may be advisable to heat the hose 4 to preventcondensation as the gases cool along the length of the tube. Currentcontinuous positive airway pressure devices can require fresh gas flowsin excess of that which can be adequately humidified. The lower freshgas flow rates used in this invention allow optimal humidification.

[0068] The mask 5 is fitted to the patient in known manner. With themask 5 in-place, the patient breathes normally. As the patient inhales,the oxygen/air mix flows from the hose 4 through the inlet 26 of themask 5 and into the patient's lungs. The slight over pressure (i.e.pressure above atmospheric) in the reservoir 8 and hose 4 makes iteasier for the patient to breathe and helps to expand the patient'slungs more fully. Further, the additional oxygen in the mix increasesthe proportion of oxygen available for uptake into the patient'sbloodstream.

[0069] Because the reservoir 8 is at a substantially constant pressure,this minimizes the pressure drop in the device when the patient inhales.

[0070] When the patient exhales, the exhaled gas is expelled through theexhaust valve 33 of the mask 5. The slight over pressure in the hose 4and reservoir 8 prevents the exhaled gases from passing back into thehose 4. The exhaust valve 33 is of known type and comprises a flap 35biased into position by a spring 36 to dose the valve against airentering through outlet 37, but to allow exhaled gases to leave throughthe valve by pressing the flap 35 in the direction of Arrow D, to openthe valve passage and allow gas to escape through outlet 37 (Arrow C).The spring 36 is selected to allow the valve to open at a predeterminedgas pressure; thereafter, the pressure remains constant and independentof the gas flow.

[0071] Because the device of the present invention can be operated atvery low flow rates (e.g. 5 litres/min), the consequences of any leaksin the system (whether from defects in the air supply hose or, morecommonly, from leaks around the face mast) could be serious to thepatient. Preferably, therefore, the circuit includes pressure sensorsand audible and/or visual alarms which are triggered if the pressurefalls below a predetermined level.

[0072] The type of exhaust valve used may be varied to suit specificapplications. At low gas flow rates, the use of an exhaust valve whichopens on expiration only (e.g. a threshold resistor valve) improvescarbon dioxide elimination and reduces the chance of rebreathing. Theuse of a valve of this type provides a circuit which has the samecharacteristics as the known “Mapleson A” circuit. The thresholdresistor valve sold under the trademark VITAL SIGNS has been foundparticularly satisfactory for preventing rebreathing.

[0073] It should be noted that the fixed orifice valves commonly used byconventional home CPAP systems are not effective at low gas flow ratesi.e. gas flow rates of between one and three times the patient's minuteventilation. However, for gas flows greater than 20 litres per minute, afixed orifice valve is satisfactory; and known types of fixed orificevalves, in combination with known variable flow generation technology,may be used with the device of the present invention.

[0074] To replace the air reservoir 8, the plate 14 is removed, and thereservoir detached from the tube 23 and lifted out of the housing 6through the port 12. The new reservoir is inserted in the same way,connected to the tube 23 and the plate 14 replaced.

[0075]FIGS. 10 and 11 illustrate an alternative form of support framing.As shown in these figures, the support framing described with referenceto FIG. 3 is replaced by framing made of hinged strips of material, asdescribed below. The support framing 7 is rectangular in plan, with twolonger members mutually parallel and secured at right angles to twoshorter members by two sets of four right angle corner pieces 15,16.

[0076] Each corner piece 15 is formed with a flat upper surface which isrigidly secured to the inner surface of the side 10. Each corner piece15 is rectangular in cross-section with the face adjacent the underlyingframing members cut away and its lower corner 17 hinged to thecorresponding underlying framing members.

[0077] Each corner piece 16 has the same shape as the correspondingcorner piece 15; the lower surface of each corner piece 16 is rigidlysecured to the inner surface of the side 9. The upper corner of eachcorner piece 16 is hinged to the corresponding framing member.

[0078] Each framing member is made up of two complimentary triangularcross-section components (see for example components 18, 19 in FIG. 11)secured together along one apex 20. In the folded down position shown inFIG. 10, the triangular cross-section components fold together to form aparallelogram in cross-section.

[0079] The above described support framing operates in the same manneras that shown in FIG. 3 and provides a rigid non distorting hinge whichpermits movement of the movable side 10 relative to be fixed side 9 onlyin a single plane, such that during its movement, side 10 always remainsparallel to side 9.

[0080] A modified version of the device is shown in FIG. 12. Except asspecifically described, this modified version is the same as the versionfirst described.

[0081] Referring to FIG. 12, an air reservoir apparatus 3 is connectedby an air supply hose 4 to a face mask 5. The air supply hose 4 may beheated by a wire 50. The air reservoir apparatus 3 has an extracompartment 51 built into the base of the housing; a multi bladed fan 52and an associated power unit are mounted in the compartment 51, giving acompact device capable of supplying air with substantially less noisethan a conventional compressor.

[0082] Air is supplied to the fan 52 through an air intake (not shown)formed in the compartment 51; the intake system may include an airfiltering system. If an air/oxygen mix is required rather than plainair, oxygen is supplied to the outlet from the compartment 51 through aninlet 53. The air or air/oxygen mix then fills the reservoir and passesthrough a humidifier 54 (optional) before entering the mask 5.

[0083] The speed of the fan 52 may be preset or manually controlled, butpreferably is controlled by pressure sensors which measure the gas flowrate from the fan 52 (e.g. by measuring a pressure drop over a fixed lowresistance) and also measure CPAP level by the patient. The sensormeasurements are used to control the speed of the fan motor in knownmanner.

[0084] It should be noted that in the equipment of the presentinvention, preferably the connectors on the ends of all of thecomponents which need to be connected together are formed so that theyare keyed to the correct connection only and cannot be incorrectlyconnected, nor can inappropriate equipment be substituted for thecorrect components. Thus, one end of the air hose 4 would be formed sothat it could be fitted only onto the outer end of the tube 23; theother end of the air hose 4 would be formed so that it could beconnected only onto the inlet 26 of the mask 5. Further, the tube 23 andthe inlet 26 would be formed so that they could accept only theconnectors on the ends of the correct type of air hose 4. Theconnections between the oxygen supply and the inlet 25 may be keyed inthe same manner.

[0085] In addition to the uses described above, the device of thepresent invention also can be used for treating a number of conditions:—

[0086] 1. The device of the present invention may be used with an aircompressor for sleep apnoea patients, who require pressurized airwithout additional oxygen. At present, the sleep apnoea apparatusconsists of a compressor and a face mask or equivalent. Since thepresent device incorporates a reservoir and low resistance hosing, itcan deliver a very constant pressure at low fresh gas flows without theneed for high and variable continuous flows which require a powerful(and therefore noisy) compressor.

[0087] 2. The device of the present invention may be used in combinationwith a suitable oxygen or air supply in the treatment of high altituderelated conditions such as acute pulmonary oedema, altitude sickness,sleep problems caused by high altitude, and breathing problems ofcritically ill patients during air transport.

[0088] 3. The device of the present invention may be used to provide alow resistance enhanced oxygen delivery device for use in hyperbaricchambers (recompression tanks), submarines, and for space medicine andhyperbaric medicine use.

[0089] 4. The device of the present invention may be used for patientswho require oxygen enriched air but whose condition is such that CPAP isthought to be unhelpful. In this case, the exhaust valve is replaced bya one-way low resistance valve, and the device is stopped open to allowthe reservoir to fill at very low pressures. This gives the patientoxygen enriched air but with a clinically insignificant level of CPAP.

[0090] 5. The device of the present invention may be used with a twolevel exhaust valve to provide two levels of CPAP pressure. Thistechnique is known; the changes in CPAP level may be automatic or timedto the patient's respiration.

[0091] It will be appreciated that the above-described device is readilyportable:—the hose 4 is disconnected from the tube 23, and compressed orcoiled. The mounting dip 92 is then pivoted until the plane of the inlet22 is parallel to the plane of the side 9. The catches 11 are used tohold the plate 10 tightly to the remainder of the housing 6. In thisfolded-down state, the device is robust and occupies little space.

1. An air reservoir apparatus for a continuous positive airway pressuredevice, the air reservoir apparatus comprising: a rigid housingprotecting an air reservoir having at least one air inlet/outlet; aplate arranged to apply a uniform pressure on the air reservoir,irrespective of the degree of inflation of the air reservoir, said platebeing connected to the housing by substantially non distortingexpandable framing, which can expand or contract to permit movement ofthe plate only in a single plane, as the air reservoir respectivelyinflates or deflates.
 2. The apparatus as claimed in claim 1, whereinsaid plate is securable to said housing when the air reservoir isdeflated, and is dimensioned and arranged to form one side of thehousing, such that the air reservoir is completely enclosed by thecombination of the plate and the housing when the plate is secured tothe housing.
 3. The apparatus as claimed in claim 1 or claim 2 whereinsaid plate is a solid sheet.
 4. The apparatus as claimed in any one ofthe preceding claims wherein said plate is formed with a sealable accessport for access to said air reservoir, such that the reservoir can beinserted and removed through said port.
 5. The apparatus as claimed inany one of the preceding claims wherein said air reservoir is made of aflexible but non-elastic material.
 6. The apparatus as claimed in claim5 wherein said air reservoir is made of a transparent material.
 7. Theapparatus as claimed in claim 5 or claim 6 wherein said air reservoir isformed with a series of concertina pleats around its periphery, suchthat the deflated reservoir can lie substantially flat but the inflatedreservoir retains its shape.
 8. The apparatus as claimed in claim 7wherein each said concertina pleat is reinforced by a stiffening rib. 9.The apparatus as claimed in claim 7, wherein the air reservoir isinternally reinforced by a series of spaced internal webs which aredesigned to be under tension when the reservoir is inflated.
 10. Theapparatus as claimed in any one of the preceding claims wherein saiduniform pressure is applied to the air reservoir by means of the plate.11. The apparatus as claimed in any one of claims 1-10, wherein at leastpart of said uniform pressure is applied to the air reservoir by meansof weights secured to the plate.
 12. The apparatus as claimed in any oneof claims 1-9 wherein said uniform pressure is applied to the airreservoir by means of a springloaded drum mounted on the side of theplate opposite to said air reservoir, the drum being connected to thehousing by non elastic cables such that the plate is biased towards thehousing and thus applies pressure to the air reservoir.
 13. Theapparatus as claimed in claim 12 wherein said springloaded drum iscalibrated so that the pressure applied to the air reservoir by theplate can be accurately adjusted.
 14. The apparatus as claimed in anyone of the preceding claims wherein said framing comprises a pair ofspaced-apart frames, the planes of the frames being parallel to eachother and perpendicular to the plane of movement of the plate; theframes being connected together by a plurality of spaced pivots whichare designed to permit relative movement of said frames only in saidplane of movement of the plate; one of said frames being rigidly securedto the plate and the other of said frames being rigidly secured to saidhousing.
 15. The apparatus as claimed in claim 14, wherein each framecomprises: a plurality of spaced blocks connected by rods rotatablysecured thereto; and each pivot comprises a pair of hinge arms, one ofsaid arms in each pair being pivoted at one end to one rod of one frameand at the other end to the other arm of that pair, and the other ofsaid arms in each pair being pivoted at one end to one rod of the otherframe and at the other end to the other arm of that pair.
 16. Theapparatus as claimed in claim 15, wherein the plate and the housing aresecured to the respective frames by means of the blocks of that frame.17. A continuous positive airway pressure device including: airreservoir apparatus as claimed in any one of claims 1-16 connected by anair supply hose to a delivery device.
 18. The device as claimed in claim17, wherein the air inlet/outlet of the air reservoir is a push-fitconnection to the air supply hose.
 19. The device as claimed in claim17, wherein the air inlet/outlet of the air reservoir is releasably heldin a mounting clip pivoted to the housing such that the plane of the airinlet/outlet may be pivoted between an out-of-use position in which saidplane lies approximately in the plane of the plate, and an in-useposition perpendicular thereto; and the air supply hose is releasablyconnectable to said mounting clip.
 20. The device as claimed in claim19, wherein in said out-of-use position, the mounting clip is arrangedto clip over the edge of the housing.
 21. The device as claimed in anyone of claims 17-20, wherein the delivery device is selected from thegroup consisting of: face mask; nasal mask; mouthpiece; endotracheal ortracheotomy tube.
 22. The device as claimed in any one of claims 17-20,wherein the delivery device comprises a face mask incorporating anexhaust valve.
 23. The device as claimed in class 22, wherein theexhaust valve is a threshold resistor valve.
 24. The device as claimedin claim 22, wherein the exhaust valve is a fixed orifice valve.
 25. Thedevice as claimed in any one of claims 17-24, wherein at least part ofthe air supply hose is heated.
 26. The device as claimed in any one ofclaims 17-25 further including a humidifier arranged to humidify atleast part of the incoming air in use.
 27. The device as claimed in anyone of claims 17-26 further including a fan arranged in use to supplyair to the reservoir at above-atmospheric pressure.
 28. The device asclaimed in any one of claims 17-27, wherein each of the connectionsbetween the components of the device is keyed to provide a uniqueconnection.
 29. The device as claimed in any one of claims 17-28,wherein the air supply hose has an internal diameter in the range 30-55mm.
 30. A method of medical treatment for any condition treatable bymeans of a metered dose inhalation agent, comprising: (1) providing acontinuous positive airway pressure device which incorporates an airreservoir apparatus as claimed in any one of claims 1-16 and which alsoincludes an air supply hose having an internal diameter in the range30-55 mm which connects the air reservoir to a face mask incorporating athreshold resistor exhaust valve; (2) connecting said device to asuitable supply of air (as hereinbefore defined); (3) connecting to saidair supply hose means for dispensing an appropriate metered doseinhalation agent at a predetermined rate; (4) administering said agentto a patient in the airstream delivered through the face mask by saiddevice.
 31. The method as claimed in claim 30, wherein said metered doseinhalation agent is selected from the group consisting of:bronchodilators; gene therapy agents; proteins; peptides;macromolecules.
 32. A method of treatment for sleep apnoea, comprising:(1) providing a continuous positive airway pressure device whichincorporates an air reservoir apparatus as claimed in any one of claims1-16 and which also includes an air supply hose having an internaldiameter in the range of 30 to 55 mm which connects the air reservoir toa delivery device; (2) connecting said device to an air compressor; (3)administering pressurized air to a patient via the delivery device. 33.A method of medical treatment of altitude sickness, acute pulmonaryodema or conditions requiring hyperbaric treatment, comprising: (1)providing a continuous positive airway pressure device whichincorporates an air reservoir apparatus as claimed in any one of claims1-16 and which also includes an air supply hose having an internaldiameter in the range 30 to 55 mm which connects the air reservoir to adelivery device; (2) connecting said CPAP device to a suitable supply ofair (as hereinbefore defined); (3) administering said air to a patientthrough said delivery device.
 34. The method as claimed in claim 33wherein said delivery device is selected from the group consisting of:face mask, nasal mask, mouthpiece, endotracheal or tracheotomy tube.